1. Field of Invention
This invention relates to a contact point type measuring device equipped with contact type encoder.
2. Description of Prior Art
Such means that the mechanical displacement of measuring members is detected as electric digital signals is well known and applied to various measuring fields as length measuring machines, position detectors, or the like. The mechanical displacement detecting means of this kind electrically detects length of a measured object as displacing amount of scale or the like. Electromagnet, electrostatic, photoelectric or various types are known as such electric detecting means, and, especially, the displacing detecting means of photoelectric conversion type is of wide and practical use as micrometers, vernier calipers, coordinate measuring machines, etc. due to the advantages of possibility of minimization and highly accurate measurement by such detecting means.
The conventional means of this type, however, has such drawbacks that it comparatively costs high and that it comparatively consumes large electric current. Since small type length measuring machines recently use batteries in order to drive the machines, it is requested that the means has long life and consumes low electric current. In the digital type displacing detector the electric process is performed by C-MOS circuits and these processing circuits consume remarkably low electric current. Contrary to this, in the photoelectric means of the conventional type, light emitters for photoelectric conversion, light emitting diodes for example, consume large electric current, which increases total consumption of electric current.
Apart from the above mentioned contactless type encoder, known is a contact point type encoder which detects electric digital signals from on and off action by contact points. The contact point type encoder has such advantage that it has simple structure and can electrically detect mechanical displacement, and is of practical use in certain fields. It is, however, used in such fields as positioning means or revolving position detector in large type driving means which does not require accuracy, and the application of the contact type is not considered in the fields, especially, in the length measuring machines, wherein small and accurate type is required. In other words, the contact point type of this kind is of low reliability and has such fundamental drawbacks that the contact conditions is extremely unstable, and long time use easily changes the contact conditions. Therefore, it is impossible for the contact point type encoder to be equipped in length measuring machines, etc. in which poor contact directly causes in error.
On the other hand, this contact point type encoder has such advantages that the voltage application can convert mechanical displacement into electric digital pulses and that no consumption of electric current is basically required. These advantages are applied to small type measuring devices which can consume low electric current and be driven by batteries by means of combining with recent voltage type elements, C-MOS transistors for example.
It is considered preferrable that the measuring device is composed of a contact point type encoder, a counter circuit section which consists of C-MOS transistors and IC's to count voltage pulses of the contact point type encoder, and a display section of measured value which consists of LCD (liquid crystal display) to display the counted value of the counter circuit as measured value. The composition of the measuring device mentioned above can provide the measuring device of low price and low current consumption.
However, since the voltage type elements of C-MOS type transistors and IC's are not suitable for high speed action, in case the measuring device is composed as described in the above, it is impossible for the measuring device to follow fast moving measuring members and there occurs error in the measured value displayed in the display section, when high frequency signals are supplied from the contact point type encoder as measured signals. Therefore, the measuring device having the composition mentioned in the above is extremely inconvenient in practical use.